Clamp-on fork lift attachments are well known in the manufacturing industry. Such fork attachments are typically mounted to the bucket of a loader, such as a front end loader or a loader backhoe, to temporarily covert the loader for use as a fork lift. Such conversions are essential on job sites where dedicated fork lifts are not available or where available fork lifts do not have sufficient size or lifting capacity to lift the relatively large or heavy loads.
For example, fork lift attachments are commonly used on construction sites for unloading trucks and lifting heavy pallets of construction materials. Fork attachments are also commonly used by farmers to convert loaders for lifting bulky or heavy items such as hay bales.
The majority of non-permanent, clamp-on fork lift attachments typically include means for mounting a rear end of each fork to a substantially flat, bottom portion or "blade" of the loader bucket which extends immediately behind a cutting edge of the bucket. These mounting means commonly include a lower bearing surface for contacting a bottom surface of the bucket blade as well as a screw-type clamping means for contacting an upper surface of the bucket blade and securing the blade against the lower bearing surface. See for example the fork attachments shown in U.S. Pat. No. 4,274,798 issued to Guest in 1981.
While the specifics of the mounting means vary with different fork attachments, all known fork attachments which use the screw-type clamps suffer from a common problem relating to damaging the loader bucket. Specifically, all known screw-type clamps tend to form a rigid connection with the blade of the loader bucket such that the clamping mechanism itself may cause significant damage to the loader bucket.
For example, the known screw-type clamps utilize a threaded rod and an opposing bar to clamp the relatively thin portion of the bucket blade to the rear of the blade cutting edge. The clamped portion of the bucket blade is thus subjected to extremely high forces at the contact points of the threaded rod and the opposing bar, and these forces may be sufficient to warp the blade or lower portion of the loader bucket. Indeed, it is not uncommon for the threaded rod to punch a hole within the relatively thin metal of the bucket blade when the screw clamp is tightened.
Prior art FIG. 8 illustrates an example of previous attempts to improve upon the design of a typical screw-type mounting clamp. A steel pad 20 is welded to a free end 22 of the threaded rod 24. However, the threaded rod 24 is constrained to only move only in the axial direction and therefore the weld connecting the pad 20 to the threaded rod 24 constrains a contact surface 26 of the pad 20 to a purely horizontal plane as shown in FIG. 8. Similarly, the bottom bearing bar 30 is typically welded to the end of the fork attachment so that its contact surface 32 is also constrained to a horizontal plane as shown in FIG. 8.
It was commonly believed that the inclusion of the pad 20 at the end 22 of the threaded rod 24 would improve the contact between the pad 20 and the blade 36 of the loader bucket by increasing the surface area which contacts the relatively thin metal of the bucket blade. However, the prior art device shown in FIG. 8 assumes that the blade or lower portion of the loader bucket will be perfectly flat when it is inserted between the upper pad 20 and the lower bearing bar 30. Unfortunately, this is typically not the case as the blade portion of the bucket will frequently be slightly angled with respect to the fork due to the varying thickness of the bucket blade. Furthermore, even if the blade or lower portion of the bucket were to be considered perfectly flat, it is not uncommon for the blade 36 to be inserted between the upper pad 20 and the lower bearing bar 30 at an angle as shown in FIG. 8.
Thus, when the prior art pad 20 is tightened down onto the upper surface 38 of the bucket blade 36, only one edge 40 of the pad 20 contacts the upper surface 38 as opposed to the entire contact surface 26 as was intended. Similarly, the angle of the blade 36 also ensures that only an edge 44 of the lower bearing bar 30 (as opposed to the entire contact surface 32) will contact a lower surface 46 of the blade 36. Therefore, the purportedly improved mounting system shown in prior art FIG. 8 exemplifies the same problems as the more conventional screw-type clamps described above, including damage to the loader bucket due to the high forces applied to the bucket blade by the limited contact surfaces (i.e., the edges 40 and 44) of the upper pad 20 and the lower bearing bar 30.
Due to the damage which is caused by prior art fork lift attachments, it is not uncommon for equipment rental companies to refuse to rent such fork lift attachments and to refuse to allow customers to use their own fork attachments on rented or leased loaders. Therefore, an improved fork lift attachment having a mounting system which will not damage the loader bucket under even the heaviest loads is needed.
It is with respect to these and other background considerations, limitations and problems, that the present invention has evolved.